1. Technical Field
The present invention relates to decoding compressed video signals, and more particularly relates to a system and method for dynamically adapting the complexity of a scaled MPEG-2 video decoder.
2. Related Art
The MPEG standards are an evolving set of standards for video and audio compression developed by the Moving Picture Experts Group (MPEG). MPEG-1 was designed for coding progressive video at a transmission rate of about 1.5 million bits per second. It was designed specifically for Video-CD and CD-i media. MPEG-2 was designed for coding interlaced images at transmission rates above 4 million bits per second. The MPEG-2 standard is used for various applications, such as digital television (DTV) broadcasts, digital versatile disk (DVD) technology, and video storage systems.
According to the MPEG-2 standard, an MPEG-2 sequence is divided into a series of GOPs (Group Of Pictures). There are three different types of pictures, with each being essentially a frame of pixels. Each GOP begins with an Intra-coded picture (I picture) followed by an arrangement of forward Predictive-coded pictures (P pictures) and Bi-directionally predictive-coded pictures (B pictures). I pictures are fields or frames coded as a stand-alone still image. P pictures are fields or frames coded relative to the nearest I or P picture, resulting in forward prediction processing. P pictures allow more compression than I pictures through the use of motion compensation, and also serve as a reference for B pictures and future P pictures. B pictures are fields or frames that use the most proximate past and future I and P picture as a reference, resulting in bi-directional prediction.
As the digital TV market gradually begins to dominate the TV market and other video applications become more desirable, the demand for systems having advanced capabilities for processing MPEG-2 pictures becomes stronger and stronger. The current emerging architecture for processing MPEG-2 data, such as that found in DTV set-top boxes and high end digital TV""s, typically utilize a combination of a digital signal processing central processing units (DSPCPU), control processors, coprocessors, and software applications. Unfortunately, even with all these resources, advanced audio/visual processing functions tend to consume more computational power than is often available.
One of the key elements in MPEG-2 processing is the MPEG-2 decoder, which converts a bitstream of compressed MPEG-2 data into pixel images. The main components of a generic MPEG-2 decoder 11 are shown in FIG. 1. There are four functional blocks: the variable length decoder (VLD) 13, inverse quantization (IQ) 15, inverse discrete cosine transform (IDCT) 17, and the motion compensation (MC) 19. Memory 21 is used to store the reference frames. The adder combines the error residuals output from IDCT 17 (path 1) with motion compensation results (path 2) to form the final video output. Unfortunately, each of these functional components consume a tremendous amount of computational power, which drives up the cost, and limits the flexibility of digital video systems using MPEG-2 technology. Accordingly, making a highly efficient, cost effective decoder remains one of the main goals of all electronics manufacturers.
One solution for addressing the processing requirements of MPEG-2 decoders is to provide specialized hardware systems that increase computational power. For example, U.S. Pat. No. 5,903,311, issued to Ozcelik et al. on May 11, 1999, which is hereby incorporated by reference, describes a chip that includes specialized circuits for an MPEG-2 decoder. Unfortunately, while overall hardware costs continue to decrease, the costs involved in designing and building specialized hardware such as this greatly drive up the expense of the decoder.
A preferred solution therefore is to implement as much functionality as possible in software, which provides significant cost and flexibility advantages over hardware solutions. In particular, software solutions reduce the need for expensive hardware, such as coprocessors, and will allow multiple video functions to run concurrently on a DSPCPU core. However, software applications tend to run too slow to handle occasions when computationally intensive decoding operations are required. Accordingly, a need exists for enhanced systems that can provide inexpensive MPEG-2 decoder solutions while maintaining an acceptable level of video quality.
This invention overcomes the above-mentioned problems, as well as others, by providing a scalable decoder system. In a first aspect, the invention provides a method for setting a threshold value for a scalable module in a video decoder, comprising the steps of: (1) decoding a first group of pictures (GOP) using an initial threshold value; (2) determining an adjusted threshold value based on the first GOP; and (3) decoding a second GOP using the adjusted threshold value.
In a second aspect, the invention provides a scalable video decoder system, comprising: a calculating system that determines an adjusted threshold value based on a previously decoded group of pictures (GOP); and a scalable module that decodes a current GOP using the adjusted threshold value.
In a third aspect, the invention provides a program product stored on a recordable media, that when executed, dynamically selects a threshold value for a scalable video decoder system, and comprises a system that determines the threshold value for a current group of pictures (GOP) based on a previously decoded GOP by iteratively selecting different threshold values until a scaled complexity of the decoder system for the previous GOP substantially meets a required complexity of the video decoder system for the current GOP.
It is therefore an advantage of the present invention to provide a system and method for dynamically setting a threshold value for a scalable module within a video decoder system.
It is therefore a further advantage to provide a scalable system that does not need to preset the threshold, and can dynamically set a scaled complexity based on the required complexity as determined by the system.